1. Field of the Invention
The invention relates in general to a wiring structure and a fabrication method thereof, and more particularly to a wiring structure for improving a crown-like defect and a fabrication method thereof.
2. Description of the Related Art
With the narrowing of the line width of copper wires, the difficulty of photo-lithography and etching process is gradually increased. Thus, misalignment or over etching phenomenon tends to occur so that the throughput of chips is decreased and the wires tend to encounter the problem of the crown-like defect. One of the reasons of generating the crown-like defect is that the copper wire has the Galvanic reaction when the exposed copper wire and the gold-plated layer on the wiring surface concurrently contact with the etchant because the copper and the gold have different oxidation potentials. In other words, the metal materials with different oxidation potentials concurrently in the etchant produce the electrochemical reaction due to the potential difference. The metal (e.g., the copper) with the high oxidation potential forms the anode, and the metal (e.g., the gold) with the low oxidation potential forms the cathode. The copper metal with the high oxidation potential forms copper ions dissolved into the etchant in the electrochemical reaction. Thus, the bottom of the copper wire is rapidly eroded to cause the crown-like defect. In addition, the copper ions in the etchant obtain the electrons and are then reproduced and deposited on the metal with the low oxidation potential, thereby darkening the color of the gold-plated layer. The above-mentioned wire etching process still has to be improved.